Light emitting diodes (LEDs) are rapidly replacing conventional sources of illumination such as incandescent bulbs. Because an LED is typically a discrete circuit, it is common to mount LEDs on circuit boards so that the LED may receive the appropriate circuit leads. Although LEDs are more efficient than conventional illumination sources, they still emit an appreciable amount of heat during operation. Metal core printed circuit boards are thus used to provide thermal management for mounted LEDs. Such a board would include a conductive core such as aluminum that is coated with a one or more dielectric layers. A printed or lithographed foil layer, such as copper, overlays the dielectric layer. The foil layer forms the electrical leads to couple to the LED. The dielectric layer(s) act to insulate the foil layer and the coupled circuits from the conductive core. Although the core is thus electrically isolated, it is still thermally connected to the LED such that it acts as an adequate heat sink.
But conventional metal core board technology is problematic for applications that must pass electrical leads through the board. For example, such a need is present in LED flashlight applications. In that regard, consider the construction of a conventional flashlight—there is an elongated cylindrical battery housing that holds the batteries and allows a user to handle the device. The battery housing connects to a flashlight head that includes a lens or transparent cover held by a bezel. At the base of the bezel is the circuit board holding the LED(s).
The circuit board is mounted within the flashlight orthogonally to the optical axis of the lens. However, such a circuit board arrangement then forms a natural barrier to the necessary electrical leads for coupling between the batteries and the board's printed foil layer (and ultimately to the LED). Conductive pins passing through the circuit board to couple to the printed foil layer need insulation from the metal core in the board to prevent the batteries from shorting out through the resulting conduction in the metal core. But an insulated pin then requires an extra soldering step to couple to the printed foil layer, which increases manufacturing costs. Alternatively, wires can be passed through a gap between the edge of the board and the bezel, which still requires an extra soldering step and requires a bigger installation space.
Accordingly, there is a need in the art for metal core circuit board configurations that enable efficient construction and soldering of leads such as conductive pins to pass through the board.